The siphuncle in Georginidae and other Ordovician actinoceroid cephalopods
Article first published online: 9 OCT 2007
Volume 10, Issue 4, pages 303–315, October 1977
How to Cite
WADE, M. (1977), The siphuncle in Georginidae and other Ordovician actinoceroid cephalopods. Lethaia, 10: 303–315. doi: 10.1111/j.1502-3931.1977.tb00625.x
- Issue published online: 9 OCT 2007
- Article first published online: 9 OCT 2007
- 21st May, 1976 (revised 15th April. 1977.
The lower Middle Ordovician carbonate sediments of the Georgina Basin in Australia contain many and varied Actinoceratida, including an endemic family, Georginidae Wade (1977), with siphuncular calcification consisting of radial lamellae separated by spaces (now sediment-filled) enclosed within calcified annulus walls. In each segment a distinct series of more massive calcareous engrafts grows inward from the inside of the connecting ring and is engrafted into adjacent annuli across the interannulus; this divides the perispatium into longitudinal perispatial sinuses. At each extremity each perispatial sinus is connected with passages leading through the segments to the axial space and, nearer to, or at the interannulus, with radial canals. Axial canals are few, but more than one is normal. Good preservation of Armenoceras and Actinoceras allows recognition of similar structures in the annuli of normal Actinoceratida.